commit 03e471c41d8b1b6eb16c9714f387449f52fe5c1d
author Fiona Ebner <f.ebner@proxmox.com> Mon Dec 18 11:13:40 2023 +0100
committer Daniel P. Berrangé <berrange@redhat.com> Fri Feb 09 12:47:58 2024 +0000
tree 4f14dd51f82a8a3c985b8ab9f1826e6d031f30e4
parent 52ed9f455ee0063958a1b18e54cab9a427fc422f

qemu_init: increase NOFILE soft limit on POSIX

In many configurations, e.g. multiple vNICs with multiple queues or
with many Ceph OSDs, the default soft limit of 1024 is not enough.
QEMU is supposed to work fine with file descriptors >= 1024 and does
not use select() on POSIX. Bump the soft limit to the allowed hard
limit to avoid issues with the aforementioned configurations.

Of course the limit could be raised from the outside, but the man page
of systemd.exec states about 'LimitNOFILE=':

> Don't use.
> [...]
> Typically applications should increase their soft limit to the hard
> limit on their own, if they are OK with working with file
> descriptors above 1023,

If the soft limit is already the same as the hard limit, avoid the
superfluous setrlimit call. This can avoid a warning with a strict
seccomp filter blocking setrlimit if NOFILE was already raised before
executing QEMU.

Buglink: https://bugzilla.proxmox.com/show_bug.cgi?id=4507
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

include/sysemu/os-posix.h

diff --git a/include/sysemu/os-posix.h b/include/sysemu/os-posix.h
index dff32ae..b881ac6 100644
--- a/include/sysemu/os-posix.h
+++ b/include/sysemu/os-posix.h
@@ -51,6 +51,7 @@
 void os_daemonize(void);
 bool os_set_runas(const char *user_id);
 void os_set_chroot(const char *path);
+void os_setup_limits(void);
 void os_setup_post(void);
 int os_mlock(void);
 

include/sysemu/os-win32.h

diff --git a/include/sysemu/os-win32.h b/include/sysemu/os-win32.h
index 1047d26..b82a5d3 100644
--- a/include/sysemu/os-win32.h
+++ b/include/sysemu/os-win32.h
@@ -128,6 +128,11 @@
     return -ENOSYS;
 }
 
+static inline void os_setup_limits(void)
+{
+    return;
+}
+
 #define fsync _commit
 
 #if !defined(lseek)

os-posix.c

diff --git a/os-posix.c b/os-posix.c
index 52ef699..a4284e2 100644
--- a/os-posix.c
+++ b/os-posix.c
@@ -24,6 +24,7 @@
  */
 
 #include "qemu/osdep.h"
+#include <sys/resource.h>
 #include <sys/wait.h>
 #include <pwd.h>
 #include <grp.h>
@@ -256,6 +257,27 @@
     }
 }
 
+void os_setup_limits(void)
+{
+    struct rlimit nofile;
+
+    if (getrlimit(RLIMIT_NOFILE, &nofile) < 0) {
+        warn_report("unable to query NOFILE limit: %s", strerror(errno));
+        return;
+    }
+
+    if (nofile.rlim_cur == nofile.rlim_max) {
+        return;
+    }
+
+    nofile.rlim_cur = nofile.rlim_max;
+
+    if (setrlimit(RLIMIT_NOFILE, &nofile) < 0) {
+        warn_report("unable to set NOFILE limit: %s", strerror(errno));
+        return;
+    }
+}
+
 void os_setup_post(void)
 {
     int fd = 0;

system/vl.c

diff --git a/system/vl.c b/system/vl.c
index 2a0bd08..95cd2d9 100644
--- a/system/vl.c
+++ b/system/vl.c
@@ -2778,6 +2778,8 @@
     error_init(argv[0]);
     qemu_init_exec_dir(argv[0]);
 
+    os_setup_limits();
+
     qemu_init_arch_modules();
 
     qemu_init_subsystems();